Machine for and method of bending tubing



Fel 2, 1943; l, F. M. KEPLER v 2,310,091,

I mammina AND Mm'aon vor' BENDING TUBING l Filgd Jan. 9, 1942 3Sheets-Sheet 1 INVENTOR.

Feb.2,1943. M. man

MACHINE FOR AND METHOD Y0F BENDING TUBING Feb. 2,` 1943. F. M. Kl-:PLER2,310,091

AND METHOD 0F BENDING TUBING snee Jui. 9, 1942 s shuts-shuts PatentedFeb. 2, 1943 M. FOR 0F BENDING *C il fi la cis M.. .Kepler, Upper Darby,Pa.

Application January '9, 19152, Serial No. 426,257

18 Cl (Cl. 153-54) The present invention relates' to a method of andapparatus for bending pipe, tubing, or the like, and it relates moreparticularlyto a method of and apparatus for forming smooth bends inpipe, tubing or the like, so, that the bent sections tubing. Stillanother object of the present invention is to provide a method forbending pipe or tubing vwithout disturbing the smooth inner wallsthereof by causing the metal of the outside walls to be displaced inaccordance with the respective lengths of the inner and outer edges ofthe curve, Another object of the present invention is to provide amethod for bending sections of pipe or tubing and, atthe same time,uniformly increasing or decreasing the inside dimensions of the pipe ortubing.

Another object of the present invention is to provide yapparatus forcarrying out4 the abovestated objects;

With the above and other objects and advantages as are apparent fromthe.y following speciilcation, appended claims and accompanying outdisturbing the inside walls of the sections,

and subsequently passing the so-corrugated sections through formingrolls thereby smoothly to bend vvsaid sections and to cause thecorrugations upon the inner edge of the bend to become deeperv and thecorrugations upon the outer edge of the bend to become shallower.

For the purpose of illustrating theI invention,A

there `are shown in the accompanying drawings forms thereof which are atpresent preferred,

give satisfactory and reliable results, although v it is to beunderstood that the various instrumentalities of which the inventionconsists can be variously arranged and organized and that the inventionis not limited to the precise arrangements and organizations of theinstrumentalities as herein shown and described.

Referring to the accompanying drawings in which like referencecharacters indicate like parts,

Figure 1 represents a frontelevational view of one embodiment of thepresent invention,

Figure Zrepresents a side elevational view of the embodiment shown inFigure 1,

Figure 3 represents a horizontal cross-sectional Y view along the line3-3 of Figure 2,

Figurev 4 represents a vertical cross-sectional view along the line 4 4of Figure 1,

Figure 5 represents a fragmentary elevational view of the driving rollshown inFigure 4; illustrating the senil-circular groove formed thereinj and the corrugations,

Figure 6 represents a cross-sectional view along the line 6--6 of'Figure 5, Figure 7 represents an elevational view of the gearing shownin Figures '1 and 3,

Figure 8 represents a view similar to that of Figure l11 represents across-sectional View ofV a sectionot tubing after it has been bent intoa 90 curve in accordance with the present invention,

Figure' l2 represents a perspective view on -a' reduced scale of thebent section shown in Figure 11, showing the appearance of the sectionalong the inner edge of the curve,

Figure 13 represents a perspective yview similar y to that of Figure 12,but showing the appearance of the bent section along the-outer edge ofthe curve.

Figure 14 represents a fragmentary cross-sectional view showing a bentsection constructed in accordance with the present invention as itappears when aillxed to a straight section.

ysince the same have 'been found in practice to .Figure 15 represents across-sectional view of'v a pipe section as' it appears during theprocess of 4 the bending; the appearance of the section during thedifferent steps 'of the process being illusing downwardly.

to that of Figure 12 but showing a section of ltubing which has beenbent through approximately 180 of arc in accordance with the presentinvention.

In one embodiment of the present invention shown in Figures 1 to 1, Imay. provide a base 20 to which are attached generally upright sideplates 2| and 22. A plurality of spacing bolts 23 connect the sideplates 2| and 22.

A drive shaft 24 passes through suitable openjings in the side plates 2|and 22 and is rotatably mounted therein and carries a driving roll 25intermediate the plates 2| and 22.

A spur gear '26 is mounted upon the end of the shaft 24 outside of andadjacent to the side plate 22 and is adapted to be driven by the worm 21"carried by the shaft 28 which is turned by the V-belt pulley 29, whichin turn may be actuated by any prime-mover. 4

A gear 30 is mounted at the other end of the the rolls (when not inoperation) by a spring- Vsupporting plate 4| which rests upon the upperedges of the side plates 2| and 22 and through rwhich the'mandrel stem40 passes. A coil spring 42 is disposed about the mandrel stem 40 abovethespring supporting plate 4|. A washer 43 is disposed about the mandrelstem 40 above the coil spring 42 and a nut 44 is screw-threadedlyattached to the uppermost end of the mandrel stem 40. When the nut 44 istightened, the coil spring 42 is compressed between the washer 43 andthe spring-supporting plate 4|, and the mandrel is thus more or lessresiliently supported intermediate the rolls when the machine is not inoperashaft 24 outside of and adjacent to the side plate i A driving roll3| is keyed to and carried by the shaft 32 which is rotatably mountedwithin the side plates 2| and 22. The driving rolls 25 and 3| havesemi-circular grooves formed about their outer peripheral edges and areso disposed that the outermost portions ofl their peripheral edgescontact each other to dene a generally circular and vertically extendingopening 33 therebetween.

A-gear'34 is mounted upon the drive shaft 32 outside of and'adacent tothe side plate 2|. The

' gear 34 meshes with the gear 30 on the shaft 24 so that the'drivmgruns 2s and 3| rotate in opposite directions at the same rate of speed;the portions -of lboth rolls defining the opening 33 mov- The grooves oftheldriving. rolls and 3| are provided with corrugations 35 extendinglperpendicularly across the grooves; `the corrugations being deepest atthe center portion of the grooves y and becoming shallower at the outeraxial edges of the grooves.

A plurality (as, for example, 3) of rolls 38 are disposed peripherallyabout the driving roll 25 upon shafts 31 joumalled within the sideplates 2| and 22. Rolls 3B are provided with generally semi-circulargrooves formed in their outer peripheries and are adapted to dennegenerally circular openings with the adjacent portions of the roll 25.Thegrooves in the rolls 35 are, prefer ably, uncorrugated.

Gears 38 may be provided upon the shafts 31 to mesh with the gear on theshaft 24 and to rotate the rolls 36 oppositely vfrom the roll 25. It ispossible. and, indeed, it may sometimes be preferred, to omit the gears38 so that the rolls' 36 are free or idle rolls.`

The rolls 36 are preferably so disposed. that. with the driving roll 3|,they provide 'a plurality of generally circular openings extending moreor tion. As will hereinafter be described, parts 4| to 44 inclusive areintended to be leftoff when the machine is in operation; the mandrellbeing held in`position by the tubing being bent under pressure of thedriving and bending rolls so that it may be considered as a free oating"mandrel.

The embodiment shown in Figure l is adapted to bend steel or other metaltubing which may be either seamless or welded tubing or pipe into asmoothly curved elbow. The final curved tubing may extend through anydesired arc by varying thelength of tubing inserted relative to the4circumferential dimension of the main drivingroll 25. Thus, the finalbent tubing may extend through more or less approximately 90 of arc asshown in Figures 11, 12 and 13 by employing a length of tubingcorresponding more or less approximately to one-quarter of thecircumference of the main drivingroll 25. By employing a section oftubing which is equal to or longer vthan half the circumference of themain driving roll 25. the nal bent tubing can extend through 180 of arc.

'Ihe operation of the presentI invention will j now be described. Thenut 44, the washer 43, the coil spring 42 and the spring supportingplate 4| are first removed from the mandrel stem 40. A length of steeltubing is then placed over the mandrel stem 40 and upon the uppermoststraight portion 46 of the mandrel 39. Parts 4| -to 44 are left off themandrel stem 40.

Power is then applied to the V-belt pulley 25 and is transmitted throughthe shaft 23, the worm 21, the spur gear 25 and the drive shaft 24 tothe driving roll 25. The power is also transmitted from the drive shaft24 through the gears 30 and 34 and the shaft 32 to the driving j roll3|. The driving rolls 25 and 3| thus rotate downwardly at the opening 33defined therebeless approximately around one-half the circumf ference ofthe driving roll 25.V

A mandrel 46 having a circularcross-section Y 1 tween. The tubing 45 iscaught by the corrugations 35 on the driving rolls 25 and 3| and isforced downwardly upon theV mandrel 39.

Since the mandrel ts snugly within the tubing 45, it is held in positionwithin the tubing 45 under pressure of the rolls 25 and 3| and may beconsidered as a. floating mandrel.

. While, in Figure 4, there is shown only a single piece of tubing 45being bent, it is possible and is contemplated to have a continuoussupply of sections 45 bent. 'I'hat is, sections 45 are inserted over themandrel stem 4l! as fast as room.

is available for them so that straight sections are set in and bentsections are removed from the machine in a continual now. These sectionsmay be of the length shown in Figure 4 so that bent sectionscorresponding to those shown in Figures 11 to 13 are obtained or thesections may be approximately twice the length shown in Figure 4 so thatbent sections extending through approximately of arc as shown in Figure16 are obtained.- Y

'i The tubing is thus forced through the annular clearance existingbetween the mandrel 39 and thev adjacent portions of the grooved drivingrolls 25 and 3l.

'I'his annular clearance is such that the metal of the outer wall of thetubing 45 is displaced by the corrugations 35 in the manner shown inFigure 14;. alternate crests and troughs being formed with the crestsextending outwardly beyond the original outer diameter of the tubingaardbei crests and troughsare changed to accommodate d5 and with thetroughs extending inwardly of j the original outer diameter of thetubing.

smoo the portion 4s of the mandrel as ntsy more or less snugly Withinthe'tublng 45, the

inner wall of the tubing remains smooth and generally unaltered inpassing through the annular clearance betweenl the driving rolls 25 and3l..

As the tubing d5 is forced further down upon the curved portion 52 of'the' mandrel 39 by the driving rolls ,and 3|, it is bent more or lesssmoothly along its axis into the curvature of the semi-circular portion52; the benttubing being forced along between the roll 25 and the rolls36 finally to emerge in the form shown in Figures 11 to 13.

As hereinabove stated, the rolls 36 may be free or idle rolls, in whichcase the subsequent movement of the bent pipe d5 is `eected by thedriving roll 25 alone. On the other hand, the rolls .33 as well as theroll 25 may be power driven as shown in Figures 1, 3 and '7 in whichcase both 'the portion of the curved `section e5 adjacent the rolls 36moves'at a somewhat greater rate of speed than that portion of thesection d5 adjacent 'the roll 25. Where this difference in speed ispronounced, as for example, where sections of tubingor pipe of largeoutside diameter are being bent, it should preferably be compensated forby rotating the rolls 3G at a somewhat higher rate of speed than theroll 25.

the change in shape of the tubing. Thus, the crests 41 and troughs 48become deeper and closer together as shown at 41-a and 48-.a due to thecompression which occurs along the inner side of the curve. On the otherhand, the crests 49 and the troughs 50 'become shallower and furtherapart as' shown at 49-a and Ell-a due to the stretching of the materialalong the outer side of the curve. l

The inner wall ofthe tubing 45 remains smooth due to the close-fittingportion 52 of the mandrel 39.

By modifying-the shape of the mandrel 3-9, and

`the clearances between the roll 25 and the rolls '36, it is possible tochange the inside diameter of the tubing during the bending operation.

Thus, if the curved portion of the mandrel is reduced in cross-sectionslightly beyond the opening 33 as shown in greatly exaggerated view at52--a in Figure 9, the inside diameter of the tubing is reducedcorrespondingly under the pressure of the roll 25 Iand the rolls 36. Onthe other hand, if the curved portion of the mandrel is increased incross-section slightly beyond the opening 33 -as shown in greatlyexaggerated view' at.

52`b in Figure 10, the tubing will be forced upon the increased portionby the driving rolls 25 and maintaining a smooth inner Wall surface andat 3i so that the inside diameter o f the tubing will vbe increasedcorrespondingly with a slight increase in the outside dimension of thetubing as well. 4

Thus, it is possible to bend the tubing d5 while the same time it ispossible to maintain the original inside diameter, or to increase theinside diameter or to decrease the inside diameter, as

desired.

Since this entire bending and shaping operation is performed cold, it isapparent that the present invention affords a rapid, inexpensive,

.and highly desirable bending step whichhas many advantages overold-type bending devices.`

In order to rotate the rolls 36 at a higher rate y meshing with the gear30 to drive the rolls 25 and 3l at the same rate of speed as hereinabovedescribed. A somewhat larger gear is alsokeyad to the outer end of theshaft 24 adjacent the` gear 30. The shafts 3l carrying the rolls 36 areregularities are presented in the path -of fluid `flow so that frictionis greatly decreased and provided with somewhat smaller gears 33--0'which mesh with and are driven by the larger gear 5i.` In this way,rolls 36 are driven at a somewhat higher rate of speed than the rolls 25and 3 i As shown in Figure 15, when the tubing 5 rst passes through theannular clearance between the portion 46 of the mandrel 3S and thedriving rolls 25 and 3l, the crests dl and troughs 48 formed by thedriving roll- 25 are generally the same size as the -crests 49 and thetroughs '50 formed by the driving roll 3|. As the tubing 5 is bent,however. the configurations of the Thus, the present invention providesa smoothly bent pipe or tubing section which has a smooth and uniforminner wall surface so that a minimum of turbulence and resistance iscreated during the passage of uid therethrough. Furthermore, the presentinvention makes it possible to bend a piece .of tubing without changingits inside characteristics or dimensions so that it can :be connected`(by welding or other means)y to a straight piece of similar tubing, asshown in Figure 14, toprovide a pipe line which is substantially uniformthroughout its entire length regardless of bends. Thus, no constrictionsor irpower loss during -nuid transmission is minimized.

While the present invention has been described in connection with thebendingof relatively short pieces of tubing or pipe, it is equally welladapted to bend a continuous relatively long length of tubing or pipe.Where a continuous length of pipe is bent, the bent portion may be cut oto the desired length. Thus, the continuous bent tubing may be cut into180 lengths or lengths or any other desired lengths.

The expression free-floating mandrel" as 'used inthe following claimsdesignates a mandrel mandrel and the rest of the machine duringoperation. t

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof, and it isAtherefore desired that the present embodiments -be considered in allrespects as'illustrative and cross-section of said tubing whereby saidtubing is enlarged in inside diameter.

4.- In a method of bending tubing or the like, the step of initiallypassing said tubing over a smooth snugly-fitting stationary mandre1 andbetween apair o f juxtaposed driving rolls, each having an annularconcave channel formed in its outer periphery, said channels havinggenerally transverse corrugations formed therein, thereby ly-ttingmandrel and through the generally v circular opening defined by a pairof juxtaposed driving rolls, each roll having an annular semicircularchannel formed in its outer periphery, said channels having generallytransverse corrugations formed therein, thereby to form diametricallyopposed series of semi-circular corrugations in the outer surface ofsaid tubing while maintaining -a smooth inner surface on said tubing,and subsequently passing the so-corrugated tubing over a curved mandrelbetween a pair of juxtaposed channeled bending rolls thereby to bendsaid tubing while deepening the corrugations along the inner edge of thebend and flattening the corrugations along the outer edge of the bendand while maintaining a smooth inner surface on said tubing.

2. A method of bending tubing or the like comprising passing the tubingover a smooth snuglyfitting mandrel and through the generally circularopening defined by a pair of juxtaposed driving rolls, each having anannular semi-circular channel formed in its outer periphery, saidchannels having generally transverse corrugations formed therein,thereby to form diametrically opposed series of semi-circularcorrugations in the outer surface of said tubing while maintain- -toform diametrically-opposed series of generally semi-circularcorrugations in the outer surface of said tubing while maintaining asmooth inner -surface on said tubing.

5. A method of bending tubing or the like comprising initially passingthe tubing over a smooth snugly-ntting mandre1 and through the generallycircular opening defined by afpair of juxtaposed driving rolls, eachhaving an annular semicircular'channel formed in its outer periphery,said channels having generally transverse corrugations formed therein,thereby to form diaing a smooth inner surface on said tubing, and lsubsequently passing the so-corrugated tubing over a curved mandrelbetween a pair of juxtaposed channeled bending rolls thereby to bendsaid tubing while deepening the corrugations along the inner edge of thebend and attening the corrugations along the outer edge of the bend andwhile maintaining a smooth inner surface on said tubing, said curvedmandrel having a crosssection somewhat smaller than the original innercross-section of said tubing whereby said tubing is reduced in insidediameter by said pair of juxtaposed channeled bending rolls.

3. A method of bending tubing or the like comprising passing the tubingover a smooth snuglytting mandrel and through the generally circularopening dened by a pair of juxtaposed driving rolls, each having anannular semi-circular channel formed in its outer periphery, said chan,-nels having generally transverse corrugations formed therein, thereby toform diametrically opposed series of semi-circular corrugations in theouter surface of said tubing while maintaining a smooth inner surface onsaid tubing, and subsequently passing the so-corrugated tubing over a`curved mandrel between a pair of juxtaposed channeled bending rollsthereby to bend said tubing while deepening the corrugations along theinner edge of the bend and flattening the corrugations along the outeredge of the bend and while maintaining a smooth inner surface'on saidtubing, said curved mandrel having a crosssection somewhat larger thanthe original inner metrically opposed series of semi-circularcorrugations in the outer surface of said tubing While maintaining asmooth -inner surface on said tubing, and subsequently passing theco-corrugated tubing over a free-oating curved mandrel between a pair ofjuxtaposed channeled bending rolls thereby to bend said tubing whiledeepening the corrugations along the inner edge of the bend and atteningthe corrugations along the outer edge of the bend and while maintaininga smooth inner surface on said tubing, and subsequently passing theso-corrugated tubing over a curved mandrel thereby to bend said tubingwhile deepening the corrugations along the inner edge of the bend andflattening the corrugations along the outer edge of the bend and whilemaintaining a smooth inner surface on said tubing.

6. A tube-bending machine comprising a central driving roll having anannular generally semi-circular channel formed in its outer periphery,said channel having generally transverse corrugations formed therein; asimilarly channeled and corrugated driving roll in juxtaposition to saidcentral driving roll and defining a generally circular forming-openingtherewith; a channeled bending roll in juxtaposition to said centraldriving roll and forming a generally circular bending-opening therewith;and a mandrel having a straight portion generally tangent to saidcentral driving roll and passing through said forming-opening and havinga curved portion continuing around said central driving roll and passingthrough said bending-opening.

7. A tube-bending machine comprising a central driving roll having anannular generally semi-circular channel formed in its outer perlph- Hery, said channel having generally transverse corrugations formedtherein; a similarly channeled and corrugated driving roll injuxtaposition to said central driving roll and defining a generallycircular forming-opening therewith; a

'channeled bending roll in juxtaposition to said ery, said channelhaving generally transverse corrugations formed therein; a similarlychanneled and corrugated driving roll in juxtaposition to said centraldriving roll and `defining a generally circular forming-openingtherewith; a channeled bending roll in juxtaposition to said centraldriving roll and forming a generally circular bending-opening therewith;and a mandrel having a straight portion generally tangent 4tosaidcentral driving roll and passing through said forming-opening and havinga curved portion continuing around said central driving roll and passingthrough said bending-opening, said curved portion having a somewhatlarger crosssection than said straight portion,

9. A tube-bending machine comprising a central driving roll having anannular generally senil-circular channel formed in its outer periphery,said channel having generally transverse corrugations formed therein; asimilarly channeled and corrugated driving roll in juxtaposition to saidvcentral driving roll and defining a generally circular forming-openingtherewith; a plurality of channeled bending rolls peripherally disposedin juxtaposition to said central driving roll and forming generallycircular bending-openings therewith; and a mandrel having a straightportion generally tangent to said central driving roll andpassingthrough said forming-opening and having a c urved portion continuingaround said central driving roll and passing through saidbending-openings.

10. A tube-bending machine comprising a central driving roll having anannular generally senil-circular channel formed in its outer. periphery,satid channel having generally transverse corrugations formed therein; asimilarly channeled and corrugated driving roll in juxtaposition to saidcentral driving roll and deining a generally circular forming-openingtherewith; -a plurality of channeled bending rolls peripherally disposedin juxtaposition to said central driving roll and forming generallycircular bendtral driving roll having an annular generallysenil-circular channel formed in its outer periphery, said channelhaving generally transverse corrugations formed therein; a similarlychanneled and corrugated driving roll Lin juxtaposition to said centraldrivingl roll and dening a generally circular forming-opening therewith;

a plurality of channeled idle rolls peripherallyI disposed in;juxtaposition to said central driving ,roll and forming generallycircular bending-openings therewitli; and a mandrel having a straightportion generally tangent to said central driving roll and passingthrough said forming-opening and having a curved portion-continuingaround said central driving roll and passing lthrough. saidbending-openings. y Y

13. A tube-bending machine comprising a.

frame; a central driving roll rotatably mounted in said frame and havingan annular generally semi-circular channel formed' in its outerperiphery, said Achannel having generally transverse corrugations formedtherein; a similarly channeled and corrugated driving roll rotatablying-openings therewith; means for driving said' juxtaposed driving rolland said bending rolls from and in conjunction with said central drivingroll; and a mandrel havinga straight portion generally tangent to saidcentral driving roll and passing through said formingopening.and

having a curved portion continuing arund said central driving roll andpassing' through said bending-openings.

li. A tube-bending machine comprising a central driving roll having anannular generally semicircular channel formed in its outer periphery,said channel having generally transverse corrugations formed therein; asimilarly channeled and corrugated driving roll in juxtaposition to saidcentral driving roll and defining a generally circular forming-openingtherewith; a plurality of channeled bending rolls periph'erally disposedin juxtaposition to said central driving mounted in said frame injuxtaposition to said central driving roll'and dening a generallycircular forming-opening therewith; a plurality of channeledbendingrolls rotatably mounted in' said iframe and peripherally disposedin juxtaposition to said central driving roll and defining generallycircular bending-openings therewith; and a mandrel supported from saidframe, said mandrel having a straight portion generally tangent 4to saidcentral driving roll and passing through said forming-opening, saidstraight portion having a smaller cross-section than saidforming-opening and providing an annular clearance therein, said mandrelhaving a curved portion continuing around said centraldriving roll andpassing through said bending-openings and forming annular clearancestherein.

' 14.' A tube-bending machine comprising a frame; a central'drivin'groll rotatably mounted in' said frame and having an annular generallysemi-circular channel formedin its outer periphery, said channel havinggenerally transverse corrugations formed therein; a similarly channeledand corrugated driving' roll rotatably mounted in said frameinjuxtaposition to said central driving roll and defining a generallycircular forming-opening therewith; a plurality oi lchanneled bendingrolls rotatably mounted in said frame and peripherally disposed injuxtaposition to said central driving roll and dening generally circularbending-openings therewith; and a mandrel resiliently'supported fromsaid frame, said mandrel having a straight portion generally tangent tosaid central driving roll and passing through said forming-opening. saidstraight portion having a smaller cross-section than saidforming-opening and providing an annular clearance therein, said mandrelhaving aV curved portion continuing around said central driving roll andpassing through said bendingopenings and forming annular clearancestherein, said curved `portion having a somewhat smaller cross-sectionthan said straight portion. f

l5. A tube-bending vmachine comprising a fram'e; a central driving rollrotatably mounted lnsaid frame and having an annular generallysemi-circular channel formed in its outer periphery, said channelhavinggenerally transverse corrugations formed therein; a similarly channeledand corrugated driving roll rotatablyl mounted in said frame injuxtaposition to said central driving roll and. defining a generallycirand a free-oating mandrel disposed within said Y frame, said mandrelhaving a straight portion generally tangent to said central driving rolland passing through said `forming-opening, said straight portion havinga smaller cross-section than said forming-opening and providing anannular clearance therein, said mandrel having a curved portioncontinuing around said central driving roll and passing through saidbendingopenings and forming annular clearances therein, said curvedportion having a somewhat larger cross-section than said straightportion.

16. A tube-bending machine comprising a frame; a central driving rollrotatably mounted in said frame and having an annular generallysemi-circular channel formed in its outer periphery, said channel havinggenerally transverse corrugations formed therein; a similarly channeledand corrugated driving roll rotatably mounted in said frame injuxtaposition to said central driving roll and defining a generally cir`cular forming-opening therewith; a plurality of channeled bending rollsrotatably mounted in said frame and peripherally disposed injuxtaposition to said central driving `roll and deining generallycircular bending-openings therewith; means carried by said frame forrotating 'said mounted in said frame in juxtaposition to said centraldriving roll and denning a generally circular forming-opening therewith;a plurality ci channeled bending rolls rotatably mounted in said frameand peripherally disposed in juxtaposition to said central driving rolland dening generally circular bending-openings therewith;

` means carried by said frame for rotating said driving rolls and saidbending rolls at predetermined speed; and a free-floating mandreldisposed within said frame, said mandrel having a in said frame andhaving an annular generally i semi-circular channel formed in its outerperiphery, said channel having generally transverse corrugations formedtherein; a similarly channeled and corrugated driving roll rotatablyjuxtaposed driving roll at the'same rate of speed as, but in theopposite direction from, the centrai-driving roll; means carried by saidframe for rotating said bending rolls at a somewhat higher rate of speedthan, and in the opposite direction from, said central driving roll; anda free-oating mandrel disposedwithin said frame, said mandrel having astraight portion generally tangent to said central driving roll andpassing through said forming-opening, said straight portion having asmaller cross-section than said forming-opening andv providing anannular clearance therein, said mandrel having a curved portioncontinuing around said central driving roll and passing through saidbending-openings and forming annular clearances therein.

18. A ltube-bending machine comprising a frame; a central driving rollrotatably mounted in said frame and having an annular generallysemi-circular channel formed in its outer periphery, said channel havinggenerally transverse corrugations formed therein; a similarly channeledand corrugated driving rcll rotatably mounted in said Iframe injuxtaposition to said central driving roll and defining a generallycircular forming-opening therewith; a plurality of vchanneled idle rollsrotatably mounted in said frame and peripherally disposed injuxtaposition to said central driving roll and deilning generallycircular bending-openings therewith; means for rotating said drivingrolls in opposite direc tions at the same rate of speed; and afree-deating mandrel disposed within said frame, said mandrel having astraight portion generally tangent to said central driving roll andpassing through said forming-opening, said straight portion having asmaller cross-section than said forming-opening and providing an annularclear ance therein, said mandrel having a curved por,- tion continuingaround said central driving roll and passing through saidbending-openings and forming annular clearances therein.

FRANCIS M. KEPLER.

